An FRP is utilized in very broad fields as a composite material having light-weight and high mechanical properties. As one method for molding such an FRP, RTM method is widely employed. In the RTM method, although the molding cycle time is relatively short, there is a case where defects called pinholes, voids, etc. remain on a surface of a molded product by a bad resin flow and the like, and in a case where the method is applied to production of a product requiring a good appearance, a surface repair step and the like is required before a painting step. From such a matter, an FRP produced by an RTM method requires time and labor for finishing the appearance, and is liable to become an expensive product.
Accordingly, various investigations have been carried out to solve such problems in the conventional RTM method. For example, Patent document 1 proposes a molding method wherein a laminated material comprising a surface layer forming material/a separation substrate with a great filtration resistance/a fibrous reinforcing material/a separation substrate with a small filtration resistance/foamable resin particles is placed in a mold used for RTM, the molding temperature is elevated, the surface layer substrate is pressed to the mold by expansion in volume of the foamable particles, and thereinto a liquid resin for molding is injected, thereby obtaining a composite molded product with a high surface quality. In this method, however, there are problems such as a problem that, because it is required to prevent the foamable particles from flowing out to the surface layer by the separation substrate with a great filtration resistance, the lamination structure is restricted, and a problem that, in order to prevent a deformation of a molded product ascribed to the inner pressure of the foamed particles after heating up to the foaming temperature of the foamable particles and molding, the temperature of the mold must be enough lowered after the liquid resin is cured, and therefore, the device increases in scale and the molding cycle time becomes long.
Further, Patent document 2 proposes a molding method wherein a random mat layer is provided just under a reinforcing fiber substrate forming a surface layer in lamination, thereby extracting bubbles from the reinforcing fiber substrate and accelerating the impregnation of resin into the reinforcing fiber substrate of the surface layer. In this method, however, because the random mat layer is disposed just under the surface substrate, bubbles contained in resin stay in the random mat layer, and there is a case where through pinholes are generated in the upper surface substrate.                Patent document 1: JP-A-7-100847        Patent document 2: JP-A-2005-232601        
It could therefore be helpful to improve productivity of a molded product by diminishing surface defects such as pinholes which have been generated on a surface layer in the conventional RTM method and reducing necessity of a repair step such as a painting step as a later step.